Field of the Invention
The present invention relates to a radiographic image photographing system and particularly, to a radiographic image photographing system photographing a plurality of radiographic images by emitting radiation onto a subject a plurality of number of times.
Description of the Related Art
In place of a conventional film/screen or stimulable phosphor plate, as a device photographing a radiographic image, a radiographic image photographing device (also called a flat panel detector, a semiconductor image sensor, or the like), in which a plurality of radiation detecting elements are arranged in a two-dimensional pattern (matrix pattern), reading electric charge generated inside each radiation detecting element as a signal value through emission of radiation has been developed.
In the conventional film/screen or stimulable phosphor plate, in a case where radiation is emitted thereonto a plurality of number of times, a problem of double exposure or multiple-exposure occurs. However, a radiographic image photographing device can continuously perform photographing, for example, by storing a detected signal value in a memory arranged inside the device or transmitting the signal value to the outside for each photographing process. In this way, by using the radiographic image photographing device, dynamic-state photographing or the like can be performed by emitting radiation to a photographing portion of a subject a plurality of number of times.
In the dynamic-state photographing, for example, in a case where photographing is performed by emitting radiation a plurality of number of times onto the chest of a patient who is a subject as a photographing portion, for example, as illustrated in FIG. 8, radiographic images (in other words, each frame image configuring a dynamic-state image of time phases T(T=t0 to t6) of a lung field R of the patient can be acquired, and, by analyzing such frame images, a maximal inspiratory level, a maximal expiratory level, an expiratory period, an inspiratory period, and the like of the lung field R can be calculated. Applications to diagnoses have been attempted by further analyzing such a dynamic-state image.
Targets to which the present invention is applied are not only such dynamic-state photographing, but also include, for example, ordinary moving-image photographing, tomosynthesis photographing, photographing using a dual energy subtraction method, and long-object photographing performed by emitting radiation a plurality of number of times while moving a radiographic image photographing device. Thus, any photographing acquiring a plurality of radiographic images by emitting radiation onto a subject a plurality of number of times is a target for the present invention.
In this way, in a case where a plurality of radiographic images are photographed by emitting radiation onto a patient who is a subject a plurality of number of times, when a dose of the emitted radiation varies for each emission, for example, in the case of the moving-image photographing, the brightness levels of frame images configuring a moving image are changed for each frame image, and it is very difficult to view the image.
In addition, for example, in the dynamic-state photographing illustrated in FIG. 8, by analyzing the brightness level of each frame image, the amount of air, the amount of the blood stream, and the like received into a lung field R, can be acquired, and such an analysis can be used for diagnoses of a ventilation function, a function of the pulmonary blood stream of the lung field R. However, since the dose of radiation emitted in each photographing process as described above varies, it cannot be determined whether the shades of the inside of each frame image are caused by the amount of air, the amount of the blood stream, or the like received into the lung field R as described above or by variations in the dose of emitted radiation, and there is a possibility that an error occurs in the diagnosis performed by viewing the dynamic-state image.
Thus, in JP 2001-305232 A, a technology for controlling the dose of radiation emitted from a radiation generating device by detecting radiation that is emitted from a radiation generating device and is transmitted through a subject or a radiographic image photographing device and feeding back the dose of detected radiation to the radiation generating device is disclosed. In addition, in JP 2002-253541 A, a technology for storing the dose (a total amount thereof) of radiation that is necessary for photographing in a radiographic image photographing device in advance and determining the dose of the radiation emitted to a subject based on the dose (a total amount thereof) and the radiation transmitted through a predetermined area of the subject is disclosed.
According to both the technologies disclosed in JP 2001-305232 A and JP 2002-253541 A, the dose of radiation emitted from the radiation generating device is adjusted by feeding back radiation after being transmitted through a subject or the like. However, by configuring as such, there is a problem at least in a case where the dynamic-state photographing (see FIG. 8) is performed.
In other words, in a case where dynamic-state photographing is performed by emitting radiation onto a subject a plurality of number of times, even when the dose of radiation emitted to the subject is the same for each photographing process, as illustrated in FIG. 8, for example, the bright level of at least a portion of the lung field R is different between the case of the maximal inspiratory level (see T=t0 or t6) and the case of the maximal expiratory level (see T=t3). In other words, the transmitted amount of radiation for the portion of the lung field R, for example, is different between the case of the maximal inspiratory level and the case of the maximal expiratory level.
Nevertheless, in a case where the dose of radiation emitted from the radiation generating device is adjusted by feeding back radiation after being transmitted through the subject (in this case, the lung field R) as described above, for example, there is not much change in the brightness level of the lung field R between the case of the maximal inspiratory level (see T=t0 or t6) and the case of the maximal expiratory level (see T=t3). For this reason, even by analyzing each frame image, the amount of air, the amount of the blood stream, or the like received into the lung field R, cannot be precisely acquired, and accordingly, a dynamic-state image (in other words, each frame image) cannot be used for diagnoses of the ventilation function, the function of the pulmonary blood stream, and the like of the lung field R.
In this way, for example, in the case of the dynamic-state photographing, in a case where the dose of radiation emitted from the radiation generating device is adjusted by feeding back the radiation after being transmitted through a subject, an image provided for a diagnosis or the like cannot be photographed. For this reason, in photographing acquiring a plurality of radiographic images by emitting radiation onto a subject a plurality of number of times including not only the dynamic-state photographing but, similarly, any other kind of photographing such as tomosynthesis photographing, it is natural to perform adjustment such that the dose of radiation emitted to a subject (in other words, the dose of radiation before being emitted to a subject) and the like are as the same as possible in each photographing process.